In a French home, the CO2 concentration in a bedroom was 4000 ppm. The bedroom size is 12 m and room height 2.5 m. Find the air change rate if two occupants were in the bedroom. Suppose that the outdoor CO2 level was 300 ppm and a person breathes out 0.30 L/min. CO2.

HVAC systems are usually serving multiple spaces that have different requirements for airflow rate of fresh air. The airflow rate requirements for the fresh (outdoor) air VD, are determined from Table 2 (Standard 62) that is presented as Table 4-5 in the textbook (M&P).

A total supply flow rate for each space Vs, is defined from heating/cooling load.

Four spaces are air-conditioned from a central AHU. The following table gives airflow rates for supply air and fresh air:

Spaces

1

2

3

4

Total

Supply air [cfm]

500

400

600

500

2000

Fresh air [cfm]

200

80

80

75

435

Fresh/Supply

0.40

0.20

0.13

0.15

0.22

Calculate the required OA fraction?

Solution:

Average fraction of OA: O OA fraction for the critical space 1:0

Corrected fraction of OA: O

The required flow rate of OA is O

Notice: X < Y <Z

435 cfm < 540 cfm < 800 cfm

Standard 62-1999 recognizes transients, i. e. high occupancy/low use spaces such as conference rooms. If the peak occupancy is used to determine required flow rate of OA, calculated Y is unnecessary high.